The subject matter disclosed herein relates to integrated circuit chips, and more specifically, to a structure and method for channel electron mobility enhancement by increasing strain in a device.
Currently, methods to improve n-type field effect transistor (NFET) complementary metal-oxide-semiconductor (CMOS) performance include stress engineering, namely a tensile strain via building in a source/drain (S/D) stressor material, e.g., carbon. Substitutional carbon induces a tensile stress that improves electron mobility in a channel of the NFET. Recent technological developments have made possible the growth of epitaxial silicon with substitutional carbon and doped with phosphorus. However, the limitations of the state of the art epitaxy include the inability to grow high concentrations of substitutional carbon and phosphorus at the same time because the two elements are competing for substitutionality.
Another limitation of an epitaxial only S/D based silicon carbon phosphorous (SiCP) system is the fact that this film can not be implanted as is, due to the displacement of the carbon atoms from substitutional positions, which leads to stress loss. The inability to implant into this film impedes resistance optimization via a higher n-type doping implant. Yet, another limitation of the epitaxial only S/D based SiCP system is the fact that this system is not compatible with the stress memorization technique (SMT), which relies on the presence of an amorphous material encapsulated with a film, preferably a tensile nitride. SMT causes a “memorization” of stress due to an expansion of silicon-based amorphous material during an anneal while encapsulated by a nitride. However, in prior art methods, the presence of substitutional carbon is not compatible with a subsequent amorphization to enable a SMT process because the amorphization will irreversibly dislocate substitutional carbon from the lattice. Incorporating carbon into substitutional sites via solid phase epitaxy (SPE) implies implants post SMT, which results in the loss of the SMT effect. In other words, the state of the art stress engineering methodology does not allow the simultaneous incorporation of substitutional carbon and a stress memorization technique.